1. Field of the Invention
The present invention relates to a thin-film magnetic head having a soft magnetic film as a core layer. In particular, the present invention relates to a thin-film magnetic head using a soft magnetic film having a high saturation magnetic flux density Ms and a low coercive force Hc.
2. Description of the Related Art
A magnetic head mounted in, for example, a hard disk has a thin-film magnetic head provided at the tip of a gimbal. This thin-film magnetic head includes an inductive write head and a MR read head.
The inductive head typically includes a lower core layer composed of a magnetic material, a nonmagnetic gap layer formed on the lower core layer, an upper core layer formed on the gap layer, and a coil layer for inducing a recording magnetic field in these core layers.
Conventional upper and lower core layers are composed of, for example, NiFe alloys (permalloy). The NiFe alloy layers are formed by electroplating. According to a conventional process, the alloy has an Fe content of approximately 45 to 55 percent by weight and exhibits a maximum saturation magnetic flux density Ms of approximately 1.5 T (tesla). However, soft magnetic films must have a higher saturation magnetic flux density, Ms, to increase recording densities.
One method for increasing the saturation magnetic flux density Ms, is to increase the Fe content. According to a conventional electroplating process using a continuous direct current, the saturation magnetic flux density Ms can be increased to approximately 1.8 T when the Fe content is increased to approximately 67 percent by weight. The saturation magnetic flux density Ms, however, cannot be increased further using this process even if the Fe content is increased further.
Moreover, the electroplating process using a continuous direct current increases the crystal grain size significantly when the Fe content exceeds approximately 62 percent by weight. These large crystal grains cause surface roughening of the film. As a result, the coercive force Hc is significantly increased.
Accordingly, it is difficult for the electroplating process using a continuous direct current to obtain a high saturation magnetic flux density Ms suitable for increasing recording densities even if the Fe content is increased in the NiFe alloy. Moreover, the coercive force Hc is undesirably increased. Both a high saturation magnetic flux density Ms and a low coercive force Hc are required for increasing recording densities.
It is an object of the present invention to provide a thin-film magnetic head suitable for high recording densities and high recording frequencies having a core layer formed of a soft magnetic film composed of a NiFe alloy exhibiting a high saturation magnetic flux density Ms and a low coercive force Hc.
A thin-film magnetic head in accordance with the present invention includes a lower core layer comprising a magnetic material, an upper core layer, a magnetic gap provided between the lower core layer and the upper core layer, the lower core layer and the upper core layer opposing each other separated by the magnetic gap at a face opposing a magnetic medium, and a coil layer inducing a recording magnetic field in the lower core layer and the upper core layer. At least one of the lower core layer and the upper core layer comprises a soft magnetic film comprising a NiFe alloy having the formula Ni1xe2x88x92xFex, an average crystal grain size of not more than 105 xc3x85, and an Fe content x in a range of 60 to 75 percent by weight.
Preferably, the average crystal grain size is not more than 100 xc3x85.
Preferably, the Fe content is at least 67 percent by weight.
The soft magnetic film has a center-line-average roughness (Ra) of preferably not more than 25 xc3x85 and more preferably not more than 15 xc3x85.
The soft magnetic film has a saturation magnetic flux density Ms of preferably at least 1.6 T, and more preferably at least 1.8 T. In the present invention, a maximum saturation magnetic flux density Ms of approximately 1.9 T is obtainable.
The soft magnetic film has a coercive force Hc of preferably not more than 1.5 Oe and more preferably not more than 1.0 Oe.
Preferably, the soft magnetic film is formed by an electroplating process using a pulsed direct current.
In the NiFe alloy film of the present invention, the average crystal grain size and the Fe content in the alloy film are optimized in order to achieve a maximum saturation magnetic flux density Ms of approximately 1.9 T, which is higher than that of a conventional NiFe alloy film. Moreover, the NiFe alloy film of the present invention exhibits a low coercive force Hc due to the optimized center-line-average roughness (Ra), the optimized average crystal grain size, and the optimized Fe content. As a result, the NiFe alloy exhibits a saturation magnetic flux density Ms of at least 1.6 T and preferably at least 1.8 T and a coercive force Hc of not more than 1.5 Oe and preferably not more than 1.0 Oe, even when the Fe content in the alloy is increased to a range of 60 percent by weight to 75 percent by weight. This NiFe alloy film is formed by the electroplating process using a pulsed direct current.
In a NiFe alloy formed by the electroplating process using the pulsed direct current, the average crystal grain size and the center-line-average roughness (Ra) of the film surface can be reduced so that both a high saturation magnetic flux density Ms and a low coercive force Hc are simultaneously achieved. The NiFe alloy film in the present invention exhibits a specific resistance which is comparable to that of a NiFe alloy film formed by a conventional electroplating process using a continuous direct current.
The thin-film magnetic having a lower core layer and/or an upper core layer composed of such a soft magnetic film is suitable for future higher recording densities and higher recording frequencies.